Method of lubricating an internal combustion engine and improving the efficiency of the emissions control system of the engine

ABSTRACT

Internal combustion engines exhibit improved efficiency of the emissions control system by using a lubricating oil composition of a base oil, an alkali or alkaline earth metal-containing detergent; a metal salt of one or more phosphorus-containing compounds represented by the formula (I), wherein X 1  and X 2  are independently O or S, and R 1  and R 2  are independently hydrocarbyl groups, the average total number of carbon atoms in R 1  and R 2  for the one or more phosphorus-containing compounds being at least 10.4; and an acylated nitrogen-containing compound having at least about 10 alphatic carbon atoms and a TBN of at least about 2; the lubricating oil composition being characterized by a phosphorus concentration of up to about 0.12% by weight and the substantial absence of copper, thereby generating a lean-phosphorus containing exhaust gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from United States ApplicationProvisional Application Ser. No. 60/388,111, filed Jun. 10, 2002.

TECHNICAL FIELD

This invention relates to a method of lubricating an internal combustionengine and improving the efficiency of the emissions control system ofthe engine.

BACKGROUND OF THE INVENTION

For decades phosphorus in the form of zinc diorgano dithiophosphates(ZDDPs) has been used as extreme pressure (EP) and antiwear additives inengine oils. A problem with the use of phosphorus, however, is that itcontaminates emissions control systems catalysts and thereby reducestheir effectiveness. In response to this problem, phosphorusconcentration has been reduced for some SAE passenger car engine oilclassifications. With the introduction of ILSAC GF-1, phosphorus levelswere limited to no more than 1200 parts per million (ppm) and with GF-3to 1000 ppm. Even at these levels of phosphorus, however, catalystcontamination is still an issue. The problem therefore is to provideadequate engine lubrication and at the same time reduce catalystcontamination. The present invention provides a solution to thisproblem.

SUMMARY OF THE INVENTION

This invention relates to a method of lubricating an internal combustionengine and improving the efficiency of the emissions control system ofthe engine, the emissions control system being equipped with a catalystcontaining exhaust gas after treatment device, the method comprising:

-   -   (A) selecting a lubricating oil composition comprising: a base        oil; an alkali or alkaline earth metal-containing detergent; a        metal salt of one or more phosphorus-containing compounds        represented by the formula

wherein in formula (I), X¹ and X² are independently O or S, and R¹ andR² are independently hydrocarbyl groups, the average total number ofcarbon atoms in R¹ and R² for the one or more phosphorus-containingcompounds being at least 10.4; and an acylated nitrogen containingcompound having at least about 10 aliphatic carbon atoms and a TBN of atleast about 2; the lubricating oil composition being characterized by aphosphorus concentration of up to about 0.12% by weight and thesubstantial absence of copper;

-   -   (B) adding the lubricating oil composition to the engine;    -   (C) operating the engine;    -   (D) generating a lean-phosphorus containing exhaust gas; and    -   (E) contacting the catalyst in the exhaust gas after treatment        device with the lean-phosphorus containing exhaust gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of the percent phosphorus retention vs. time observedfor Examples C-1 and 1.

DETAILED DESCRIPTION OF THE INVENTION

The term “hydrocarbyl,” when referring to groups attached to theremainder of a molecule, refers to groups having a purely hydrocarbon orpredominantly hydrocarbon character within the context of thisinvention. Such groups include the following:

(1) Purely hydrocarbon groups; that is, aliphatic, alicyclic, aromatic,aliphatic- and alicyclic-substituted aromatic, aromatic-substitutedaliphatic and alicyclic groups, and the like, as well as cyclic groupswherein the ring is completed through another portion of the molecule(that is, any two indicated substituents may together form an alicyclicgroup). Examples include methyl, octyl, cyclohexyl, phenyl, etc.

(2) Substituted hydrocarbon groups; that is, groups containingnon-hydrocarbon substituents which do not alter the predominantlyhydrocarbon character of the group. Examples include hydroxy, nitro,cyano, alkoxy, acyl, etc.

(3) Hetero groups; that is, groups which, while predominantlyhydrocarbon in character, contain atoms other than carbon in a chain orring otherwise composed of carbon atoms. Examples include nitrogen,oxygen and sulfur.

In general, no more than about three substituents or hetero atoms, andin one embodiment no more than one, will be present for each 10 carbonatoms in the hydrocarbyl group.

The term “lower” as used herein in conjunction with terms such ashydrocarbyl, alkyl, alkenyl, alkoxy, and the like, is intended todescribe such groups which contain a total of up to 7 carbon atoms.

The term “oil-soluble” refers to a material that is soluble in mineraloil to the extent of at least about 0.5 gram per liter at 25° C.

The term “TBN” refers to total base number. This is the amount of acid(perchloric or hydrochloric) needed to neutralize all or part of amaterial's basicity, expressed as milligrams of KOH per gram of sample.

The term “high molecular weight phosphorus containing compound” refersto one or more compounds represented by formula (I) wherein the averagetotal number of carbon atoms in R¹ and R² for the one or more compoundsis at least 10.4, and in one embodiment, at least 10.8.

The term “low molecular weight phosphorus containing compound” refers toone or more compounds represented by formula (I) wherein the averagetotal number of carbon atoms in R¹ and R² for the one or more compoundsis less than 10.4.

The term “lean-phosphorus containing exhaust gas” refers to an exhaustgas that is generated in an internal combustion engine lubricated with alubricating oil composition containing a metal salt of a high molecularweight phosphorus containing compound, the exhaust gas having arelatively low concentration of phosphorus when compared to an exhaustgas generated under the same conditions using the same lubricating oilcomposition containing the same level of phosphorus except that thephosphorus containing compound is a low molecular weight phosphoruscontaining compound.

The term “substantial absence of copper” refers to the fact that copperis not intentionally added to the lubricating oil composition used withthe inventive method and, if present, is present as an impurity, theconcentration of this impurity at the time the lubricating oilcomposition is added to the engine being no more than about 10 ppm, andin one embodiment no more than about 5 ppm, and in one embodiment nomore than about 2 ppm.

The term “substantial absence of magnesium” refers to the fact that, inone embodiment of the invention, magnesium is not intentionally added tothe lubricating oil composition used with the inventive method and, ifpresent, is present as an impurity, the concentration of this impurityat the time the lubricating oil composition is added to the engine beingno more than about 100 ppm, and in one embodiment no more than about 50ppm, and in one embodiment no more than about 25 ppm, and in oneembodiment no more than about 15 ppm.

The Inventive Method

The inventive method provides for lubricating an internal combustionengine while at the same time improving the efficiency of the emissionscontrol system used with the engine. The lubricating oil composition isselected from those lubricating oil compositions that generate alean-phosphorus containing exhaust gas during operation of the engine.The lean-phosphorus containing exhaust gas is advanced to the emissionscontrol system. In the emissions control system the lean-phosphoruscontaining exhaust gas contacts the catalyst used in the exhaust gasafter treatment device. The phosphorus in the lean-phosphorus containingexhaust gas contaminates the catalyst and thereby reduces itsefficiency. However, since the level of phosphorus in thelean-phosphorus containing exhaust gas is at a reduced level, the amountof contamination of the catalyst is reduced. This reduction incontamination results in an improvement in the efficiency of theemissions control system.

The generation of a lean-phosphorus containing exhaust gas is dependenton proper selection of the lubricating oil composition used to lubricatethe engine. The lubricating oil composition used with the inventivemethod contains an alkali or alkaline earth metal containing detergent,a metal salt of at least one phosphorus-containing compound representedby formula (I), and an acylated-nitrogen containing compound. Thiscombination of additives, at least in one embodiment of the invention,provides a synergistic combination resulting in a reduction in thevolatility of the phosphorus used in the lubricating oil composition.Additional optional nitrogen-containing compounds (e.g., antioxidants)when present may also contribute to this synergistic effect. Thisreduction in phosphorus volatility provides for the generation of alean-phosphorus containing exhaust gas with the inventive method. In oneembodiment of the invention, the weight ratio of detergent metal tophosphorus in the lubricating oil composition at the time thelubricating oil composition is added to the engine is from about 0.5:1to about 10:1, and in one embodiment about 2:1 to about 4:1, and in oneembodiment about 2.5:1 to about 3:1. In one embodiment, the weight ratioof nitrogen to phosphorus in the lubricating oil composition at the timethe lubricating oil composition is added to the engine is about 0.3:1 toabout 4:1, and in one embodiment about 0.5:1 to about 2:1, and in oneembodiment about 1:1 to about 1.5:1.

The amount of phosphorus in the exhaust gas during the operation of theengine is indirectly proportional to the amount of phosphorus retainedin the lubricating oil composition in the crankcase. The amount ofphosphorus retained in the crankcase can be calculated from thefollowing formula:

${\%\mspace{14mu} P_{retention}} = {\left\lbrack \frac{\left( {\%\mspace{14mu}{wt}\mspace{14mu} P_{drain}} \right)\left( {\%\mspace{14mu}{wt}\mspace{14mu} M_{new}} \right)}{\left( {\%\mspace{14mu}{wt}\mspace{14mu} P_{new}} \right)\left( {\%\mspace{14mu}{wt}\mspace{14mu} M_{drain}} \right)} \right\rbrack \times 100}$wherein: % wt P_(drain) is the percent by weight of phosphorus in thelubricating oil composition in the crankcase at the end of a draininterval; % wt M_(new) is the percent by weight of detergent metal inthe lubricating oil composition in the crankcase at the beginning of thedrain interval; % wt P_(new) is the percent by weight of phosphorus inthe lubricating oil composition in the crankcase at the beginning of thedrain interval; and % wt M_(drain) is the percent by weight of detergentmetal in the lubricating oil composition at the end of the draininterval. In one embodiment of the invention, the amount of phosphorusretained in the crankcase oil of the engine after a 12000 kilometer(7500 mile) drain cycle is at least about 80% by weight, and in oneembodiment at least about 84% by weight, and in one embodiment at leastabout 88% by weight, and in one embodiment at least about 92% by weight,and in one embodiment at least about 95% by weight, and in oneembodiment at least about 98% by weight. In one embodiment of theinvention, the amount of phosphorus lost from the crankcase oil with theexhaust gas over a 7500 mile (12000 kilometer) drain cycle is about 20%by weight or less, and in one embodiment about 16% by weight or less,and in one embodiment about 12% by weight or less, and in one embodimentabout 8% by weight or less, and in one embodiment about 5% by weight orless, and in one embodiment about 2% by weight or less.

It has been unexpectedly discovered that the use of copper in thelubricating oil composition tends to increase the volatility of thephosphorus used therein. Accordingly, at the time the lubricating oilcomposition used with the inventive method is added to the engine it ischaracterized by the substantial absence of copper.

It has also been unexpectedly discovered, at least in one embodiment ofthe invention, that the use of magnesium in the lubricating oilcomposition tends to increase the volatility of the phosphorus usedtherein. Accordingly, in one embodiment of the invention, at the timethe lubricating oil composition used with the inventive method is addedto the engine it is characterized by the substantial absence ofmagnesium.

The Internal Combustion Engine

The internal combustion engine that may be operated in accordance withthe invention may be any internal combustion engine that is equippedwith an emissions control system that utilizes a catalyst containingexhaust gas after treatment device. These include engines that employ aclosed crankcase system and positive crankcase ventilation. The internalcombustion engine may be a spark-ignited or a compression-ignitedengine. These engines include automobile and truck engines, two-cycleengines, aviation piston engines, marine and railroad diesel engines,and the like. Included are on- and off-highway engines. Thecompression-ignited engines include those for both mobile and stationarypower plants. The compression-ignited engines include those used inurban buses, as well as all classes of trucks. The compression-ignitedengines may be of the two-stroke per cycle or four-stroke per cycletype. The compression-ignited engines include heavy duty diesel engines.

The exhaust gas after treatment device may be referred to as a catalyticconverter and may be of any conventional design. The exhaust aftertreatment device may be comprised of flow-through passages of ceramic ormetal coated with a washcoat comprised of zeolite, Al₂O₃, SiO₂, TiO₂,CeO₂, ZrO₂, V₂O₅, La₂O₃, or mixtures of two or more thereof, thewashcoat supporting a catalyst selected from the group consisting of Pt,Pd, Rh, Ir, Ru, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ag, Ce, Ga, or a mixtureof two or more thereof.

The Lubricating Oil Composition.

The lubricating oil composition used in accordance with the inventivemethod is comprised of one or more base oils which are generally presentin a major amount. The base oil may be present in an amount greater thanabout 60%, and in one embodiment greater than about 70%, and in oneembodiment greater than about 80% by weight, and in one embodimentgreater than about 85% by weight of the lubricating oil composition. Thelubricating oil composition contains: an alkali or alkaline earth metalcontaining detergent; a metal salt of at least one phosphorus-containingcompound represented by formula (I) which typically functions as anantiwear agent, EP additive, corrosion inhibitor and/or antioxidant; andan acylated-nitrogen containing compound which typically functions as adispersant. The lubricating oil composition may contain other additivesknown in the art.

The lubricating oil composition may have a viscosity of up to about 16.3mm²/s (cSt) at 100° C., and in one embodiment about 5 to about 16.3mm²/s (cSt) at 100° C., and in one embodiment about 6 to about 13 mm²/s(cSt) at 100° C.

The lubricating oil composition may have an SAE Viscosity Grade of 0W,0W-20, 0W-30, 0W-40, 0W-50, 0W-60, 5W, 5W-20, 5W-30, 5W-40, 5W-50,5W-60, 10W, 10W-20, 10W-30, 10W-40 or 10W-50. The viscosity grade may beSAE 15W-40, SAE 20, SAE 30, SAE 40 or SAE 20W-50.

The lubricating oil composition may be characterized by a sulfur contentof up to about 1% by weight, and in one embodiment up to about 0.5% byweight.

The lubricating oil composition may be characterized by a phosphoruscontent of up to about 0.12% or up to about 0.10% or up to about 0.08%or up to about 0.05% by weight, and in one embodiment about 0.03 toabout 0.12% by weight, and in one embodiment about 0.03 to about 0.10%by weight, and in one embodiment about 0.03 to about 0.08% by weight,and in one embodiment about 0.03 to about 0.05% by weight.

The ash content of the lubricating oil composition as determined by theprocedures in ASTM D-874-96 may be in the range of about 0.3 to about1.4% by weight, and in one embodiment about 0.3 to about 1.2% by weight,and in one embodiment about 0.3 to about 1.0% by weight.

The lubricating oil composition may be characterized by a chlorinecontent of up to about 100 ppm, and in one embodiment up to about 50ppm, and in one embodiment up to about 10 ppm.

The Base Oil

The base oil used in the lubricating oil composition may be selectedfrom any of the base oils in Groups I-V as specified in the AmericanPetroleum Institute (API) Base Oil Interchangeability Guidelines. Thefive base oil groups are as follows:

Base Oil Viscosity Category Sulfur (%) Saturates (%) Index Group I >0.03 and/or  <90 80 to 120 Group II ≦0.03 and ≧90 80 to 120 Group III≦0.03 and ≧90 ≧120 Group IV All polyalphaolefins (PAOs) Group V Allothers not included in Groups I, II, III or IVGroups I, II and III are mineral oil base stocks.

The base oil may be a natural oil, synthetic oil or mixture thereof. Thenatural oils include animal oils and vegetable oils (e.g., castor oil,lard oil) as well as mineral lubricating oils such as liquid petroleumoils and solvent treated or acid-treated mineral lubricating oils of theparaffinic, naphthenic or mixed paraffinic-naphthenic types. Oilsderived from coal or shale are also useful.

Synthetic oils include hydrocarbon oils such as polymerized andinterpolymerized olefins, alkylbenzenes, polyphenyls, alkylated diphenylethers, alkylated diphenyl sulfides, and derivatives, analogs andhomologs thereof. The synthetic oils include alkylene oxide polymers andinterpolymers and derivatives thereof where the terminal hydroxyl groupshave been modified by esterification, etherification, etc.; esters ofdicarboxylic acids (e.g., phthalic acid, succinic acid, alkyl succinicacids, alkenyl succinic acids, etc.) with a variety of alcohols (e.g.,butyl alcohol, hexyl alcohol, dodecyl alcohol, 2-ethylhexyl alcohol,ethylene glycol, etc.); and esters made from C₅ to C₁₂ monocarboxylicacids and polyols or polyol ethers.

In one embodiment, the base oil may be a polyalphaolefin (PAO) or an oilderived from Fischer-Tropsch synthesized hydrocarbons. In otherembodiments Group II or group III oils or mixtures thereof can be used,as well as Group III or mixtures of Group III and Group IV oils.

Unrefined, refined and rerefined oils, either natural or synthetic (aswell as mixtures of two or more of any of these) of the type disclosedhereinabove can be used as the base oil.

The Alkali or Alkaline Earth Metal Containing Detergent

The alkali metal or alkaline earth metal containing detergent may be analkali or alkaline earth metal salt of an acidic organic compound. Theacidic organic compound may be an organic sulfur acid, carboxylic acidor derivative thereof, phenol or hydrocarbyl substituted saligenin. Theacidic organic compound may be a linear oligomer or polymer containingunsubstituted or substituted phenol units and unsubstituted orsubstituted salicylic acid units. These salts may be neutral oroverbased. The former contain an amount of metal cation just sufficientto neutralize the acidic groups present in the salt anion; the lattercontain an excess of metal cation and are often termed basic, overbased,hyperbased or superbased salts. These salts may have a TBN in the rangeof about 30 to about 460, and in one embodiment about 100 to about 400,and in one embodiment about 200 to about 400, and in one embodimentabout 300 to about 400.

The organic sulfur acids may be oil-soluble organic sulfur acids such assulfonic, sulfamic, thiosulfonic, sulfinic, sulfenic, partial estersulfuric, sulfurous and thiosulfuric acid. Generally they are salts ofaliphatic or aromatic sulfonic acids. The sulfonic acids include themono- or poly-nuclear aromatic or cycloaliphatic compounds.

The carboxylic acids include aliphatic, cycloaliphatic, and aromaticmono- and polybasic carboxylic acids such as the naphthenic acids,alkyl- or alkenyl-substituted cyclopentanoic acids, alkyl- oralkenyl-substituted cyclohexanoic acids, alkyl- or alkenyl-substitutedaromatic carboxylic acids. The aliphatic acids generally contain atleast about 8 carbon atoms, and in one embodiment at least about 12carbon atoms. Usually they have no more than about 400 carbon atoms. Thecycloaliphatic and aliphatic carboxylic acids can be saturated orunsaturated.

A useful group of carboxylic acids are the oil-soluble aromaticcarboxylic acids. These acids may be represented by the formula:(R*)_(a)-Ar*(CXXH)_(m)  (II)wherein in Formula (II), R* is an aliphatic hydrocarbyl group of about 4to about 400 carbon atoms, a is an integer of from one to four, Ar* is apolyvalent aromatic hydrocarbon nucleus of up to about 14 carbon atoms,each X is independently a sulfur or oxygen atom, and m is an integer offrom one to four with the proviso that R* and a are such that there isan average of at least about 8 aliphatic carbon atoms provided by the R*groups for each acid molecule.

A useful group of carboxylic acids are the aliphatic-hydrocarbonsubstituted salicylic acids wherein each aliphatic hydrocarbonsubstituent contains an average of at least about 8 carbon atoms, and inone embodiment at least about 16 carbon atoms per substituent, and theacids contain one to three substituents per molecule. A usefulaliphatic-hydrocarbon substituted salicylic acid is C₁₆-C₁₈ alkylsalicylic acid. A group of carboxylic acid derivatives that are usefulare the lactones represented by the formula

wherein in Formula (III), R¹, R², R³, R⁴, R⁵ and R⁶ are independently H,hydrocarbyl groups or hydroxy substituted hydrocarbyl groups of from 1to about 30 carbon atoms, with the proviso that the total number ofcarbon atoms must be sufficient to render the lactones oil soluble; R²and R³ can be linked together to form an aliphatic or aromatic ring; anda is a number in the range of zero to 4. A useful lactone can beprepared by reacting an alkyl (e.g., dodecyl) phenol with glyoxylic acidat a molar ratio of about 2:1.

Neutral and basic salts of phenols (generally known as phenates) arealso useful in the compositions of this invention and well known tothose skilled in the art. The phenols from which these phenates areformed are of the general formula(R*)_(a)-(Ar*)-(OH)_(m)  (IV)wherein in Formula (IV), R*, a, Ar*, and m have the same meaning asdescribed hereinabove with reference to Formula (II).

The hydrocarbyl-substituted saligenins may be represented by the formula

wherein in Formula (V): each X independently is —CHO or —CH₂OH; each Yindependently is —CH₂— or —CH₂OCH₂—; wherein the —CHO groups comprise atleast about 10 mole percent of the X and Y groups; each M isindependently a valence of an alkali or alkaline earth metal ion; each Ris independently a hydrocarbyl group containing 1 to about 60 carbonatoms; m is 0 to about 10; n is 0 or 1 provided that when n is 0 the Mis replaced with H; and each p is independently 0, 1, 2, or 3; providedthat at least one aromatic ring contains an R substituent and that thetotal number of carbon atoms in all R groups is at least 7; and furtherprovided that if m is 1 or greater, then one of the X groups can be —H.n may have an average value of about 0.1 to about 10, and in oneembodiment about 2 to about 9. Each R may contain about 7 to about 28carbon atoms, and in one embodiment about 9 to about 18 carbon atoms.

The linear oligomers or polymers containing phenol units and salicylicunits may contain m units of formula (VI-A)

and n units of the formula (VI-B)

joined together, each end of the compound having a terminal group whichis independently one of the following

wherein in formulae (VI-A) to (VI-D): Y is a divalent bridging groupwhich may be the same or different in each unit; R⁰ is hydrogen or ahydrocarbyl group; R⁵ is hydrogen or a hydrocarbyl; j is 1 or 2; R³ ishydrogen, a hydrocarbyl or a hetero-substituted hydrocarbyl group;either R¹ is hydroxyl and R² and R⁴ are independently either hydrogen,hydrocarbyl or hetero-substituted hydrocarbyl, or R² and R⁴ are hydroxyland R¹ is either hydrogen, hydrocarbyl or hetero-substitutedhydrocarbyl; and the number of units of structures VI-A and VI-B is atleast 1. In one embodiment, m is at least 1; n is at least 2; the ratioof m to n ranges from about 0.1:1 to about 2:1; the total of m+n is atleast 3. The total of m+n may range from 3 to about 50, and in oneembodiment 3 to about 20. The ratio of m to n may range from about 0.1:1to about 1:1, and in one embodiment about 0.1:1 to about 0.5:1. Each Ymay independently be represented by the formula (CHR⁶)_(d) in which R⁶is either hydrogen or hydrocarbyl and d is an integer which is atleast 1. In one embodiment, R⁶ contains 1 to about 6 carbon atoms. Inone embodiment, d is from 1 to about 4. Y may optionally be sulfurrather than (CHR⁶)_(d) in up to 50% of the units, such that the amountof sulfur incorporated in the molecule is up to 50 mole % of the Ygroups. In one embodiment, the amount of sulfur is between 8 and 20 mole%, and in one embodiment the compound is sulfur-free. R⁰ may be ahydrocarbyl (e.g., alkyl) group of 1 to about 6 carbon atoms. R⁵ may bea hydrocarbyl group of 1 to about 100 carbon atoms, and in oneembodiment 1 to about 30 carbon atoms, and in one embodiment 1 to about6 carbon atoms. R³ may be a hydrocarbyl of 1 to about 100 carbon atoms,and in one embodiment 1 to about 30 carbon atoms. R³ may behetero-substituted. The hetero atoms or groups may be —O— or —NH—. Inone embodiment, Y is CH₂; R¹ is hydroxyl; R² and R⁴ are hydrogen; R³ isa hydrocarbyl group of about 6 to about 60 carbon atoms, and in oneembodiment about 6 to about 18 carbon atoms; R⁰ is hydrogen; R⁵ ishydrogen; j is 1; and m+n has a value of at least 5; and m is 1 or 2.

Mixtures of two or more neutral or basic metal salts of the hereinabovedescribed acidic organic compounds may be used in the lubricating oilcompositions.

The alkali and alkaline earth metals that are useful include sodium,potassium, lithium, calcium, strontium and barium, with sodium, lithiumand calcium being especially useful.

It has been unexpectedly discovered, at least in one embodiment of theinvention, that the use of sodium in the lubricating oil compositiontends to decrease the volatility of the phosphorus used thereinsignificantly. Accordingly, in one embodiment of the invention, the useof sodium as the detergent metal is particularly useful.

It has been unexpectedly discovered, at least in one embodiment of theinvention, that the use of magnesium in the lubricating oil compositiontends to increase the volatility of the phosphorus used therein.Accordingly, in one embodiment of the invention, the detergent metal isnot magnesium.

The alkali or alkaline earth metal containing detergent may be employedin the lubricating oil composition at a concentration in the range ofabout 0.1 to about 10% by weight, and in one embodiment about 0.2 toabout 5% percent by weight, and in one embodiment about 0.3% to about 3%by weight, and in one embodiment about 0.5 to about 2% by weight.

The Phosphorus-Containing Metal Salt

The phosphorus-containing compound useful in making thephosphorus-containing metal salt may be one or more compoundsrepresented by the formula

wherein in Formula (I): X¹ and X² are independently oxygen or sulfur,and R¹ and R² are independently hydrocarbyl groups, the average totalnumber of carbon atoms in R¹ and R² for the one or morephosphorus-containing compounds being at least 10.4, and in oneembodiment at least 10.8, and in one embodiment at least about 11, andin one embodiment at least about 11.5, and in one embodiment at leastabout 12. In one embodiment, the average total number of carbon atoms inR¹ and R² for the one or more phosphorus-containing compounds may be upto about 100, and in one embodiment up to about 60, and in oneembodiment up to about 24. In one embodiment less than 34 mole percentof all the R¹ and R² hydrocarbyl groups supplied by all thephosphorus-containing metal salt(s) (especially, zincdialkylthiophosphates) in the composition contain 4 or fewer carbonatoms or, alternatively, contain 3 or fewer carbons. In otherembodiments, less that 40 mole percent or less than 36 or 31 molepercent of all such hydrocarbyl groups contain 4 or fewer or 3 or fewercarbon atoms. R¹ and R² may be independently hydrocarbyl groups of about3 to about 50 carbon atoms, or about 3 to about 12 or about 3 to about10 carbon atoms, and in one embodiment about 4 to about 50 carbon atoms,and in one embodiment about 5 to about 50 carbon atoms, and in oneembodiment about 6 to about 50 carbon atoms. R¹ and R² may beindependently alkyl groups, alkenyl groups, aromatic groups, or mixturesof two or more thereof. R¹ and R² may be derived from one or moreprimary alcohols, one or more secondary alcohols, or a mixture of atleast one primary alcohol and at least one secondary alcohol. In certainembodiments, greater than 60 mole percent, for instance, at least 70mole percent or at least 73 mole percent, of all the R¹ and R² groupssupplied by the phosphorus-containing metal salt are derived fromsecondary alcohols. R¹ and R² may be the same as each other, althoughthey may be different and either or both may be mixtures. Examples of R¹and R² include isopropyl, 4-methyl-2-pentyl, isooctyl, 2-ethylhexyl,decyl, dodecyl, tetradecyl, dodecenyl, phenyl, naphthyl, alkylphenyl,alkylnaphthyl, phenylalkyl, naphthylalkyl, alkylphenylalkyl,alkylnaphthylalkyl, and mixtures thereof.

In one embodiment, the phosphorus-containing compound is adialkyldithiophosphate derived from 4-methyl-2-pentyl alcohol.

In one embodiment, two or more phosphorus-containing compounds are usedin the lubricating oil composition and at least about 80% by weight, andin one embodiment at least about 90% by weight, and in one embodiment atleast about 95% by weight, and in one embodiment at least about 98% byweight, of the phosphorus present in the lubricating oil composition atthe time the lubricating oil composition is added to the engine ispresent in a compound represented by formula (I) wherein R¹ and R²independently are hydrocarbyl groups (e.g., alkyl or alkenyl) of about 6to about 18 carbon atoms.

In one embodiment, the following mixture of phosphorus-containingcompounds is used: about 70 to about 99 molar percent of adialkyldithiophosphate derived from 4-methyl-2-pentyl alcohol; and about1 to about 30 molar percent of a dialkyldithiophosphate derived from analcohol mixture of about 60% by mole isopropyl alcohol and about 40% bymole 4-methyl-2-pentyl alcohol.

The metal salts of the phosphorus-containing compounds represented byformula (I) include those salts containing Group IA, IIA or IIB metals,aluminum, lead, tin, iron, molybdenum, cobalt, nickel or bismuth. Zincis an especially useful metal. In one embodiment, the metal is notmagnesium. These salts can be neutral salts or overbased salts.

The phosphorus-containing metal salt may be employed in the lubricatingoil composition at a concentration sufficient to provide the lubricatingoil composition with a phosphorus concentration in the range of up toabout 0.12% by weight, and in one embodiment about 0.03 to about 0.12%percent by weight, and in one embodiment about 0.03% to about 0.10% byweight, and in one embodiment about 0.03 to about 0.08% by weight, andin one embodiment about 0.03 to about 0.05% by weight.

The Acylated Nitrogen Containing Compound

The acylated nitrogen containing compound may be made by reacting atleast one carboxylic acid acylating agent with an amino compound. Theacylating agent may be linked to the amino compound through an imido,amido, amidine or salt linkage. The substituent comprised of at leastabout 10 aliphatic carbon atoms may be in either the carboxylic acidacylating agent derived portion of the molecule or in the amino compoundderived portion of the molecule.

Illustrative substituent groups containing at least about 10 aliphaticcarbon atoms include n-decyl, n-dodecyl, tetrapropylene, n-octadecyl,oleyl, chlorooctadecyl, triicontanyl, etc. Generally, these substituentsare hydrocarbyl groups made from homo- or interpolymers (e.g.,copolymers, terpolymers) of mono- or di-olefins having 2 to about 10carbon atoms, such as ethylene, propylene, 1-butene, isobutene,butadiene, isoprene, 1-hexene, 1-octene, etc. Typically, these olefinsare 1-monoolefins. The substituent may also be derived from thehalogenated (e.g., chlorinated or brominated) analogs of such homo- orinterpolymers.

A useful source for the substituent groups are poly(isobutene)s obtainedby polymerization of a C₄ refinery stream having a butene content ofabout 35 to about 75 weight percent and an isobutene content of about 30to about 60 weight percent in the presence of a Lewis acid catalyst suchas aluminum trichloride or boron trifluoride. These polybutenes containpredominantly isobutene repeating units.

In one embodiment, the substituent is a polyisobutene group derived froma polyisobutene having a high methylvinylidene isomer content, that is,at least about 50% methylvinylidene, and in one embodiment at leastabout 70% methylvinylidene. Suitable high methylvinylidenepolyisobutenes include those prepared using boron trifluoride catalysts.

The acylating agent can vary from formic acid and its acyl derivativesto acylating agents having high molecular weight aliphatic substituentsof up to about 5,000, 10,000 or 20,000 carbon atoms. In one embodiment,the acylating agent is a hydrocarbyl substituted succinic acid oranhydride containing hydrocarbyl substituent groups and succinic groupswherein the substituent groups are derived from a polyalkene such aspolyisobutene. The acid or anhydride may be characterized by thepresence within its structure of an average of at least about 0.9succinic group for each equivalent weight of substituent groups, and inone embodiment about 0.9 to about 2.5 succinic groups for eachequivalent weight of substituent groups. The polyalkene may have numberaverage molecular weight ( Mn) of at least about 700, and in oneembodiment about 700 to about 3000, and in one embodiment about 900 toabout 2200. The ratio between the weight average molecular weight (Mw)and the (Mn) (that is, Mw/Mn) may range from about 1 to about 10, and inone embodiment about 1.5 to about 5, and in one embodiment about 2.5 toabout 5. For purposes of this invention, the number of equivalentweights of substituent groups is deemed to be the number correspondingto the quotient obtained by dividing the Mn value of the polyalkene fromwhich the substituent is derived into the total weight of thesubstituent groups present in the substituted succinic acid oranhydride.

The amino compound may be characterized by the presence within itsstructure of at least one HN< group and can be a monoamine or polyamine.Mixtures of two or more amino compounds can be used in the reaction withone or more acylating reagents. In one embodiment, the amino compoundcontains at least one primary amino group (i.e., —NH₂). In oneembodiment, the amine is a polyamine, for example, a polyaminecontaining at least two —NH— groups, either or both of which are primaryor secondary amines. The amines may be aliphatic, cycloaliphatic,aromatic or heterocyclic amines. Hydroxy substituted amines, such asalkanol amines (e.g., mono- or diethanol amine), and hydroxy(polyhydrocarbyloxy) anologs of such alkanol amines may be used.

Among the useful amines are the alkylene polyamines, including thepolyalkylene polyamines. The alkylene polyamines include thoserepresented by the formula

wherein in Formula (VII), n is from 1 to about 14; each R isindependently a hydrogen atom, a hydrocarbyl group or ahydroxy-substituted or amine-substituted hydrocarbyl group having up toabout 30 atoms, or two R groups on different nitrogen atoms can bejoined together to form a U group, with the proviso that at least one Rgroup is a hydrogen atom and U is an alkylene group of about 2 to about10 carbon atoms. U may be ethylene or propylene. Alkylene polyamineswhere each R is hydrogen or an amino-substituted hydrocarbyl group withthe ethylene polyamines and mixtures of ethylene polyamines are useful.Usually n will have an average value of from about 2 to about 10. Suchalkylene polyamines include methylene polyamines, ethylene polyamines,propylene polyamines, butylene polyamines, pentylene polyamines,hexylene polyamines, heptylene polyamines, etc. The higher homologs ofsuch amines and related amino alkyl-substituted piperazines are alsoincluded.

Alkylene polyamines that are useful include ethylene diamine, diethylenetriamine, triethylenel, tetramine, tetraethylene pentamine,pentaethylene hexamine, propylene diamine, trimethylene diamine,hexamethylene diamine, decamethylene diamine, octamethylene diamine,di(heptamethylene) triamine, tripropylene tetramine, trimethylenediamine, di(trimethylene)triamine, N-(2-aminoethyl)-piperazine,1,4-bis(2-aminoethyl)piperazine, and the like. Higher homologs such asthose obtained by condensing two or more of the above-illustratedalkylene amines may be used. Mixtures of two or more of any of theafore-described polyamines may be used.

Useful polyamines include those resulting from stripping polyaminemixtures. In this instance, lower molecular weight polyamines andvolatile contaminants are removed from an alkylene polyamine mixture toleave as residue what is often termed “polyamine bottoms”. In general,alkylene polyamine bottoms can be characterized as having less thanabout 2% by weight, and in one embodiment less than about 1% by weightmaterial boiling below about 200° C.

The acylated nitrogen containing compounds include amine salts, amides,imides, amidines, amidic acids, amidic salts and imidazolines as well asmixtures thereof. To prepare the acylated nitrogen-containing compoundsfrom the acylating agents and the amino compounds, one or more acylatingreagents and one or more amino compounds may be heated, optionally inthe presence of a normally liquid, substantially inert organic liquidsolvent/diluent, at temperatures in the range of 80° C. up to thedecomposition point of any of the reactants or the product but normallyat temperatures in the range of about 100° C. to about 300° C., provided300° C. does not exceed the decomposition point of any of the reactantsor the product. Temperatures of about 125° C. to about 250° C. may beused. The acylating agent and the amino compound may be reacted inamounts sufficient to provide from about 0.5 to about 3 moles of aminocompound per equivalent of acylating agent. The number of equivalents ofthe acylating agent will vary with the number of carboxy groups presenttherein. In determining the number of equivalents of the acylatingagent, those carboxyl functions which are not capable of reacting as acarboxylic acid acylating agent are excluded. In general, however, thereis one equivalent of acylating agent for each carboxy group in theacylating agent.

It has been unexpectedly discovered, in at least one embodiment of theinvention, that the use of acylated nitrogen containing compounds withrelatively high TBNs in the lubricating oil composition tend to reducethe volatility of the phosphorus used therein. Accordingly, in oneembodiment of the invention, the acylated nitrogen containing compoundhas a TBN of at least about 2, and in one embodiment from about 2 toabout 30, and in one embodiment from about 5 to about 30, and in oneembodiment about 10 to about 20.

The acylated nitrogen containing compound may be employed in thelubricating oil composition at a concentration in the range of about 1to about 20% by weight, and in one embodiment about 1 to about 10%percent by weight, and in one embodiment about 1% to about 5% by weight.

Additional Lubricating Oil Additives

The lubricating oil composition may also contain other lubricantadditives known in the art. These include, for example,corrosion-inhibiting agents, antioxidants, viscosity modifiers,dispersant viscosity index modifiers, pour point depressants, frictionmodifiers, antiwear agents other than those discussed above, EP agentsother than those discussed above, dispersants other than those discussedabove, detergents other than those discussed above, fluidity modifiers,copper passivators, anti-foam agents, etc. Each of the foregoingadditives, when used, is used at a functionally effective amount toimpart the desired properties to the lubricant. Generally, theconcentration of each of these additives, when used, ranges from about0.001% to about 20% by weight, and in one embodiment about 0.01% toabout 10% by weight based on the total weight of the lubricating oilcomposition.

Concentrates and Diluents

The foregoing lubricating oil additives can be added directly to thebase oil to form the lubricating oil composition. In one embodiment,however, one or more of the additives are diluted with a substantiallyinert, normally liquid organic diluent such as mineral oil, syntheticoil, naphtha, alkylated (e.g., C₁₀-C₁₃ alkyl) benzene, toluene or xyleneto form an additive concentrate. These concentrates usually contain fromabout 1% to about 99% by weight, and in one embodiment 10% to 90% byweight of such diluent. The concentrates may be added to the base oil toform the lubricating oil composition.

EXAMPLES C-1 AND 1

Engine tests using the Sequence IIIF Test Procedure are conducted usingthe lubricating oil compositions identified in Table 1. Example 1 iswithin the scope of the invention, while Example C-1 is not within thescope of the invention but is provided for purposes of comparison. InTable I, unless otherwise indicated, all numerical values are in percentby weight.

TABLE I Example C-1 1 Base oil: Mixture of two Group II base oils (1)4.5 mm²/s (cSt) @ 100° C., wt % 90 90 (2) 6.0 mm²/s (cSt) @ 100° C., wt% 10 10 Combined base oil viscosity, mm²/s (cSt) @ 100° C. 4.6 4.6Combined base oil concentration 81.35 81.22 Viscosity modifier: LZ7070Davailable from Lubrizol 8.00 8.00 identified as olefin copolymerdispersed in oil (91% diluent oil) Pour point depressant: LZ7742available from 0.15 0.15 Lubrizol identified as a methacrylate copolymerdispersed with oil (35% diluent oil) Dispersant: succinimide derivedfrom polyisobutene 5.10 5.10 (Mn = 2000) substituted succinic anhydrideand polyethylene amines dispersed in oil, TBN = 15 (45% diluent oil)Diluent oil 0.50 0.50 EP/antiwear additive: zinc dialkyl dithiophosphate0.73 — derived from 60% iso-propyl alcohol and 40% 4- methyl-2-pentylalcohol, TBN = 5 (9% diluent oil) EP/antiwear additive: zinc dialkyldithiophosphate — 0.86 derived from 4-methyl-2-pentyl alcohol, TBN = 5(8% diluent oil) Antioxidant: nonylated diphenyl amine 1.0 1.0Antioxidant: sulfurized olefin containing 13.9% sulfur 0.44 0.44dispersed with oil (5% diluent oil) Antioxidant: butyl acrylatesubstituted di-t-butyl 1.2 1.2 phenol Detergent: calcium sulfonatedispersed in oil, 0.88 0.88 TBN = 300 (42% diluent oil) Detergent:calcium sulfonate dispersed in oil, 0.65 0.65 TBN = 400 (42% diluentoil) Antifoam agent: polydimethylsiloxane dispersed in oil 89 ppm 89 ppm(87.5% diluent oil) Viscosity Grade 5W-30 5W-30 Chemical analysis of oilat start of test Ca 0.1925 0.1947 P 0.0764 0.0685

During the course of each engine test the concentration of calcium andphosphorus in the crankcase oil is measured every ten hours. From thesemeasurements the percent by weight of phosphorus retained in thecrankcase (% P_(retention)) is calculated using the following formula:

${\%\mspace{14mu} P_{retention}} = {\left\lbrack \frac{\left( {\%\mspace{14mu}{wt}\mspace{14mu} P_{t}} \right)\left( {\%\mspace{14mu}{wt}\mspace{14mu} M_{new}} \right)}{\left( {\%\mspace{14mu}{wt}\mspace{14mu} P_{new}} \right)\left( {\%\mspace{14mu}{wt}\mspace{14mu} M_{t}} \right)} \right\rbrack \times 100}$wherein:

% wt P_(t) is the percent by weight of phosphorus in the lubricating oilcomposition in the crankcase at the end of t hours of testing using theSequence III F Test Procedure;

% wt M_(new) is the percent by weight of calcium in the lubricating oilcomposition in the crankcase at the beginning of testing using theSequence III F Test Procedure;

% wt P_(new) is the percent by weight of phosphorus in the lubricatingoil composition in the crankcase at the beginning of testing using theSequence III F Test Procedure; and

% wt M_(t) is the percent by weight of calcium in the lubricating oilcomposition at the end of t hours of testing using the Sequence III FTest Procedure.

The results of these engine tests are shown in FIG. 1. which is a plotof % P_(retention) vs. time for each engine test. These results indicatea significant improvement in phosphorus retention for the lubricatingoil composition used in Example 1 as compared to the lubricating oilcomposition used in Example C-1. The amount of phosphorus retained inthe crankcase during operation of the engine is an indirect measurementof the amount of phosphorus lost from the crankcase with the exhaustgas. For example, in Example 1, after 50 hours of testing, 86.7% byweight of the phosphorus is retained in the crankcase oil, while 13.3%by weight is carried away with the exhaust gas. Similarly, with ExampleC-1, after 50 hours of testing, 69.2% by weight of the phosphorus isretained in the crankcase oil, while 30.8% is carried away with theexhaust gas. The exhaust gas generated in Example 1 is a lean-phosphoruscontaining exhaust gas, while the exhaust gas generated in Example C-1is not a lean-phosphorus containing exhaust gas.

EXAMPLES 2-7

A series of lubricant formulations are prepared; each comprising:

about 84.5 percent by weight oil, predominantly API Group II base oils,overall viscosity 4.5 mm²/s (cSt) at 100° C.;

5 percent (including customary diluent oil) of olefin copolymerviscosity modifier(s);

0.15 percent (including diluent oil) of polymeric pour pointdepressant(s);

5.1 percent (including diluent oil) of succinimide dispersant(s);

0.4 percent of friction modifier(s);

2.0 percent antioxidant(s);

1.5 percent (including diluent oil) of overbased calcium and sodiumdetergents;

0.15 percent of molybdenum-containing antioxidant/friction modifier(s);

0.35 percent of corrosion inhibitor(s); and

100 ppm of commercial antifoam agent(s).

Each formulation also contains one or more zinc dialkyldithiophosphateEP/antiwear agents (“ZDPs”), in each instance providing 0.076 percent byweight phosphorus. The amounts and types of the ZPDs, in weight percenton an oil free-basis, are indicated in Table II.

TABLE II Ex: 2 3* 4 5 6* 7 ZDP #1 0.18 — — — 0.69 0.30 ZDP #2 0.61 —0.27 0.41 — 0.47 ZDP #3 — 0.77 0.52 0.39 — — Mole % of “R” groups: C3 1660 40 30 60 26 C6 84 — 33 50 40 74 C8 — 40 27 20 — — Avg. C perphosphorus 11.05 10.00 10.64 11.00 8.40 10.44 acid moiety PEI (mg P/Loil) 15 45 30 19 39 16 *A comparative example ZDP #1 - prepared usingisopropanol (C3) and 4-methyl-2-pentanol (C6) (both secondary alcohols).ZDP #2 - prepared using 4-methyl-2-pentanol ZDP #3 - prepared usingisopropanol and 2-ethylhexanol (a C8 primary alcohol). The Mole % of “R”groups is the mole percent of all the hydrocarbyl groups having theindicated carbon number provided by all the ZDP component(s).

Also presented in Table II are the results of the Phosphorus EmissionsIndex Test (PEI) for each sample, expressed in terms of mg phosphorusper liter of oil. This test is based on the Selby modification of theNoack volatility test (ASTM D 5800), in which volatilized oil andphosphorus are collected in the receiver section of a Selby-Noackapparatus and the collected materials subjected to inductively-coupledplasma spectroscopy to determine the phosphorus concentration. The testis further described in T. W. Selby, “Development and significance ofthe Phosphorus Emission Index of Engine Oils,” presented at 13^(th)International Colloquium Tribology—Lubricants, Materials, andLubrication, Technische Akademie Esslingen, Stuttgart/Osffildern,Germany, Jan. 15-17, 2002, available athttp://www.savantgroup.com/PhosIndx-v2.PDF. Lower PEI values areconsidered better, and values of 20 or below are considered particularlygood.

The results show that those samples with ZDP having on average 10.4carbon atoms per phosphorus acid moiety exhibit lower phosphorusemissions. Those samples for which, additionally, the mole percent ofhydrocarbyl groups supplied by the ZDP of C4 or less, is less than 34percent, exhibit the lowest phosphorus emissions.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

1. A method of lubricating an internal combustion engine and improvingthe efficiency of the emissions control system of the engine, theemissions control system being equipped with a catalyst containingexhaust gas after treatment device, the method comprising: (A) selectinga lubricating oil composition comprising: a base oil; an alkali oralkaline earth metal-containing detergent; a metal salt of one or morephosphorus-containing compounds represented by the formula

wherein in formula (I), X¹ and X² are independently O or S, and R¹ andR² are independently hydrocarbyl groups, the average total number ofcarbon atoms per phosphorus-containing moiety being at least 10.4,wherein at least one of the R¹ and R² groups in one or more of thephosphorus-containing compounds contains 4 or fewer carbon atoms and upto about 40 percent of all the R¹ and R² groups supplied by thephosphorus-containing metal salt contain 4 or fewer carbon atoms; and anacylated nitrogen containing compound having at least about 10 aliphaticcarbon atoms and a TBN of at least about 2; the lubricating oilcomposition being characterized by a phosphorus concentration of up toabout 0.12% by weight and the substantial absence of copper; (B) addingthe lubricating oil composition to the engine; (C) operating the engine;(D) generating a lean-phosphorus containing exhaust gas; and (E)contacting the catalyst in the exhaust gas after treatment device withthe lean-phosphorus containing exhaust gas.
 2. The method of claim 1wherein during step (A) the weight ratio of detergent metal tophosphorus in the lubricating oil composition is from about 0.5:1 toabout 10:1.
 3. The method of claim 1 wherein the lubricating oilcomposition has a viscosity of up to about 16.3 mm²/s (cSt) at 100° C.4. The method of claim 1 wherein the base oil comprises a mineral oil.5. The method of claim 1 wherein the base oil comprises apoly-alpha-olefin or an oil derived from Fischer-Tropsch synthesizedhydrocarbons or mixtures thereof.
 6. The method of claim 1 wherein informula (I), X¹ and X² are each S, and one of R¹ and R² is an alkyl oralkenyl group of about 6 to about 18 carbon atoms.
 7. The method ofclaim 1 wherein in formula (I), X¹ and X² are each S, and one of R¹ andR² is an aromatic group.
 8. The method of claim 1 wherein the metal usedin the metal salt of a phosphorus containing compound is zinc.
 9. Themethod of claim 1 wherein at least about 80% by weight of the phosphoruspresent in the lubricating oil composition is present in a compoundrepresented by formula (I) wherein one of R¹ and R² is a hydrocarbylgroup of about 6 to about 18 carbon atoms.
 10. The method of claim 1wherein the alkali or alkaline earth metal-containing detergent is asalt of an organic sulfur acid, carboxylic acid, lactone, phenol, orhydrocarbyl substituted saligenin.
 11. The method of claim 1 wherein thealkali or alkaline earth metal-containing detergent is a salt of alinear oligomer or polymer containing unsubstituted or substitutedphenol units and unsubstituted or substituted salicylic units.
 12. Themethod of claim 1 wherein the alkali or alkaline earth metal is sodium,lithium or calcium.
 13. The method of claim 1 wherein the acylatednitrogen-containing compound is derived from a carboxylic acylatingagent and at least one amino compound containing at least one —NH—group, the acylating agent being linked to the amino compound through animido, amido, amid me or salt linkage.
 14. The method of claim 1 whereinthe acylated nitrogen containing compound is a polyisobutene substitutedsuccinimide.
 15. The method of claim 1 wherein the lubricating oilcomposition further comprises a dispersant, corrosion-inhibiting agent,antioxidant, viscosity modifier, dispersant viscosity index modifier,pour point depressant, friction modifier, anti-wear agent, extremepressure agent, fluidity modifier, copper passivator, anti-foam agent,or a mixture of two or more thereof.
 16. The method of claim 1 whereinthe lubricating oil composition is characterized by the substantialabsence of magnesium.
 17. A method of lubricating an internal combustionengine and improving the efficiency of the emissions control system ofthe engine, the emissions control system being equipped with a catalystcontaining exhaust gas after treatment device, the method comprising:(A) selecting a lubricating oil composition comprising: a base oil; analkali or alkaline earth metal-containing detergent, the alkali oralkaline earth metal being sodium, lithium or calcium; a zinc salt of aphosphorus-containing compound represented by the formula

wherein R¹ and R² independently hydrocarbyl groups, the average totalnumber of carbon atoms per phosphorus-containing moiety being at least10.4, wherein at least one of the R¹ and R² groups in one or more of thephosphorus-containing compounds contains 4 or fewer carbon atoms and upto about 40 percent of all the R¹ and R² groups supplied by thephosphorus-containing metal salt contain 4 or fewer carbon atoms; atleast about 80% by weight of the phosphorus present in the lubricatingoil composition being present in a compound represented by formula (II)wherein one of R¹ and R² is a hydrocarbyl group of about 6 to about 18carbon atoms; and a polyisobutene substituted succinimide having a TBNof about 5 to about 30, the polyisobutene substituent having a numberaverage molecular weight in the range of about 700 to about 3000; thelubricating oil composition being characterized by a phosphorusconcentration of no more than about 0.12% by weight and the substantialabsence of copper; (B) adding the lubricating oil composition to theengine; (C) operating the engine; (D) generating a lean-phosphoruscontaining exhaust gas; and (E) contacting the catalyst in the exhaustgas after treatment device with the lean-phosphorus containing exhaustgas.
 18. The method of claim 1 wherein less than 34 mole percent of allthe R¹ and R² groups supplied by the phosphorus-containing metal saltcontain 4 or fewer carbon atoms.
 19. The method of claim 1 wherein thelubricating oil composition is characterized by a phosphorus content ofup to about 0.08 percent by weight phosphorus.
 20. The method of claim 1wherein from about 16 to about 34 percent of all the R¹ and R² groupssupplied by the phosphorus-containing metal salt contain 4 or fewercarbon atoms.
 21. The method of claim 1 wherein up to about 40 percentof all the R¹ and R² groups supplied by the phosphorus-containing metalsalt contain 4 or fewer carbon atoms and at least 60 mole percent of allthe R¹ and R² groups supplied by the phosphorus-containing metal saltare derived from secondary alcohols.
 22. The method of claim 1 whereinabout 16 to about 34 percent of all the R¹ and R² groups supplied by thephosphorus-containing metal salt contain 4 or fewer carbon atoms and atleast 60 mole percent of all the R¹ and R² groups supplied by thephosphorus-containing metal salt are derived from secondary alcohols.23. A method of lubricating an internal combustion engine and improvingthe efficiency of the emissions control system of the engine, theemissions control system being equipped with a catalyst containingexhaust gas after treatment device, the method comprising: (A) selectinga lubricating oil composition comprising: a base oil; an alkali oralkaline earth metal-containing detergent; a metal salt of one or morephosphorus-containing compounds represented by the formula

wherein in formula (I), X¹ and X² are independently O or S, and R¹ andR² are independently hydrocarbyl groups, the average total number ofcarbon atoms per phosphorus-containing moiety being at least 10.4,wherein at least one of the R¹ and R² groups in one or more of thephosphorus-containing compounds contains 4 or fewer carbon atoms and upto about 40 percent of all the R¹ and R² groups supplied by thephosphorus-containing metal salt contain 4 or fewer carbon atoms, and atleast 60 mole percent of all the R¹ and R² groups supplied by thephosphorus-containing metal salts are derived from secondary alcohols;and an acylated nitrogen containing compound having at least about 10aliphatic carbon atoms and a TBN of at least about 2; the lubricatingoil composition being characterized by a phosphorus concentration of upto about 0.12% by weight and the substantial absence of copper; (B)adding the lubricating oil composition to the engine; (C) operating theengine; (D) generating a lean-phosphorus containing exhaust gas; and (E)contacting the catalyst in the exhaust gas after treatment device withthe lean-phosphorus containing exhaust gas.